1、PDF外文：http:/ Engineering and Design 84 (2009) 17081712 Contents lists available at ScienceDirect Fusion Engineering and Design journal homepage: Thermal structural analysis of SST-1 vacuum vessel and cryostat assembly using ANSYS Prosenjit Santr
2、a a, , Vijay Bedakihale a , Tata Ranganath b a Institute for Plasma Research, Bhat, Gandhinagar 382428, Gujarat, India b Tractebel Engineers & Constructors Pvt. Ltd., New Delhi, India a r t i c l e i n f o a b
3、 s t r a c t Article history: Available online 25 February 2009 Keywords: Vacuum vessel Cryostat Baking ANSYS Steady state super-conducting tokamak-1 (SST-1) is a medium sized tokamak, which has been designed to produce a D shaped double null div
4、ertor plasma and operate in quasi steady state (1000 s). SST-1 vacuum system comprises of plasma chamber (vacuum vessel, interconnecting rings, baking and cooling channels), and cryostat all made of SS 304L material designed to meet ultra high vacuum requirements for plasma generation and connement.
5、 Prior to plasma shot and operation the vessel assembly is baked to 250/150 C from room temperature and discharge cleaned to remove impurities/trapped gases from wall surfaces. Due to baking the non-uniform temperature pattern on the vessel assembly coupled with atmospheric pressure loading and self
6、-weight give rise to high thermal-structural stresses, which needs to be analyzed in detail. In addition the vessel assembly being a thin shell vessel structure needs to be checked for critical buckling load caused by atmospheric and baking thermal loads. Considering symmetry of SST- 1, 1/16th of th
7、e geometry is modeled for nite element (FE) analysis using ANSYS for different loading scenarios, e.g. self-weight, pressure loading considering normal operating conditions, and off-normal loads coupled with baking of vacuum vessel from room temperature 250 C to 150 C,
8、buckling and modal analysis for future dynamic analysis. The paper will discuss details about SST-1 vacuum system/cryostat, solid and FE model of SST-1, different loading scenarios, material details and the stress codes used. We will also present the thermal structural results of FE analysis u
9、sing ANSYS for various load cases being investigated and our observations under different loading conditions. 2009 Elsevier B.V. All rights reserved. 1. Introduction Steady state super-conducting tokamak-1 (SST-1) (Fig. 1) is a medium &nbs
10、p;sized experimental tokamak device for production and connement of double null D shaped divertor plasma and operate in quasi steady state (1000 s). Vacuum vessel (VV) Vacuum vessel of SST-1 1,2 is an all welded SS 304L structure designed to meet ultra
11、 high vacuum (UHV) requirements for plasma generation and connement. Each vessel module is made up of one wedge shape sector along with a radial port, two (top and bottom) vertical ports and one interconnecting ring. Entire structure con- sists of 16 wedge shaped sectors which in turn are welded tog
12、ether by 16 interconnecting rings (ICRs) to form a complete torus. The poloidal (elevation) cross-section of vessel/torus is close to “D” shape. The VV, ICR and ports are baked (250150 C) by circulating hot pressurized nitrogen gas in the rectangular channels welded to Corresponding au
13、thor. Tel.: +91 7923962125/2126； fax: +91 7923962277. E-mail address: prosenjitipr.res.in (P. Santra). the inner wall of VV, ICR and ports. The hot nitrogen enters the sys- tem through two inlet headers, covers different part of VV/ICR/ports and exits through two outlet headers. Cryostat (CS)
14、 SST-1 cryostat is a 16-sided polygon shaped outer VV made of SS 304L which encloses plasma chamber (VV) TF/PF coils and LN2 thermal radiation shields. Cryostat provides high vacuum barrier around plasma VV and surrounding cold mass and isolates super conducting coils from ambient pressure and
15、 temperature. Cryostat has openings for 16 radial ports, and 32 vertical ports of SST-1. It is mounted on a base frame and provides structural support for VV, in-vessel components, cooling circuits and cold mass. 2. SS 304L material property details The details of the structural material
16、 SS 304L of which the SST-1 VV/CS is made of are mentioned in Table 1. As a post-fabrication FE analysis is being attempted with existing material test reports, tensile/yield stress, elongation values, from material test reports are considered here. 0920-3796/$ see front matter 2009 Elsevier B
17、.V. All rights reserved. doi:10.1016/j.fusengdes.2009.01.042 P. Santra et al. / Fusion Engineering and Design 84 (2009) 17081712 1709 Fig. 1. Iso metric cut view of SST-1. 3. Solid and nite element (FE) model of VV/CS The thermal structural analysis of SST-1 VV/CS wa
18、s carried out using nite element package ANSYS 3. As SST-1 VV/CS is symmetric in toroidal direction (16 identical ports/cryostat) with symmetric loadings, only 1/16th 4,5 is modeled for coupled thermal structural analysis taking advantage of mirror symme- try thereby reducing
19、 model size and minimum use of computer resources. Only the portion of the baking channels welded to the VV/ring is considered for analysis. 3D thermal Shell 57 and 3D Shell 41 were chosen for thermal analysis and structural analysis for meshing areas. 3D Link 34 for thermal convection analysis and
20、3D Beam 4 were chosen for structural analysis of baking channels. The 1/16th solid model (Fig. 2a) has 463 key-points, 654 lines and 231 areas while the 1/16th FE model (Fig. 2b) has 8948 nodes and 16,379 elements. The thickness of various components of VV/CS as input for real constants of she
21、ll and beam in ANSYS elements is mentioned in Table 2. 4. Boundary and loading conditions Boundary conditions (BC) As 1/16th is modeled for FE analysis therefore symmetric BC was applied at outer most edges of ICRs, lip joints, cryostat and support column. Symmetric BC implies tha
22、t in plane rotations and out of plane translations are zero. Also the base and top of inner wall of Table 1 Material properties of SS 304L. SI. no. Material specications Typical values Fig. 2. (a) Solid model of SST-1 VV/CS and (b) FE model of SST-1 VV/CS. cryo
23、stat and column base are completely restrained in all DOF to prevent any un-constrained movement. Baking channels in rings and vessel sector are completely restrained in all DOF to prevent any unconstrained movement. Table 2 1 Youngs Modulus (N/mm2 ) 196200 Thickness of various VV/CS component
24、s of SST-1. SI. no. Component/geometry name Thickness (mm) 2 Poissions ratio 0.29 3 Density (kg/mm3 ) 0.8E-05 1 Vessel sector 10 4 Coefcient of thermal expansion (mm/mm/ C) 5 Thermal conductivity (W/mm K) 17 1006 0.0163 and 0.0214 at 25 C and 500 C 2 Vessel port bed 06 3 Vessel port ang
25、e 30 4 Vessel top and bottom port 06 5 Vessel interconnecting ring 10 6 Lip joint 03 6 Specic heat (J/kg K) 500 and 563 at 25 C and 400 C 7 Emissivity 0.11 (polished surface) 8 Tensile strength (MPa) 554 (from material test certicate) 9 Yield strength (MPa) 281 (from material test certicate) 10 Elon
26、gation (%) 44 (from material test certicate) 7 Cryostat base 10 8 Cryostat top and bottom port 08 9 Cryostat inboard wall 05 10 Cryostat support column 12.7 11 Baking channels (B H T) 16 8 2 1710 P. Santra et al. / Fusion Engineering and Design 84 (2009) 17081712 Table 3 ASME stress code. Stre
27、ss category Limit based on yield stress SY (Von Mises criteria) Limit based on allowable stress intensity Sm (Tresca criteria) General primary membrane stress intensity (Pm ) 2/3 of SY Sm Local membrane stress intensity (PL ) 1SY 1.5Sm Primary membrane + primary bending stress (PL + PB ) 1SY 1.5Sm P
28、rimary + secondary stress intensity (PL + PB + Q) 2SY 3.0Sm Thermal analysis loadings Uniform (reference) temperature of the VV/CS assembly was kept at 25 C. Transient thermal analysis to obtain temperature plot assuming convection between hot nitrogen gas and vessel wall beneath channe
29、ls and conduction along vessel wall for 720 min 43,200 s and estimate time required reaching steady state. The heat transfer co-efcient of hot nitrogen gas was estimated at 269 W/m2 K using DittusBoeltus co-relation. The junction at the VV ports (top, bottom and radial)
30、 with CS is maintained at 25 C so that the CS is at 25 C and does not get heated up by conduc- tion. The thermal analysis was carried out for bulk temperatures of hot nitrogen gas at 250 C and 150 C i.e. VV and ring are baked to 250 C and 150 C from room temperature of 25 C and estimate the thermal
31、stresses induced at these temperatures. For simplicity of analysis radiation effects are ignored in the present case. The num- ber of SST-1 baking cycles will be around 100 (occasionally) in its entire lifetime. Structural loadings Structural loadings includes self (dead) weight of rela
32、ted SST-1 components due to gravity, g = 9.81 m/s2 and 760 Torr (0.1 N/mm2) pressure on cryostat due to atmosphere external loading on CS, vacuum inside VV and ring i.e. pressure difference across vessel wall/ring is zero. So the total loading is the atmospheric pressure loading combined with
33、baking of VV/ring and self-weight the com- ponents. 5. Stress code used In general for structural-ductile material like SS 304 L allowable (design) stress intensity Sm is lesser of 2/3 of yield stress (SY) or 1/3 of ultimate tensile stress (SU) as mentioned in ASME Boiler and Pressure Ve
34、ssel Code Section VIII, Division 2 6. The stress category details for primary and secondary stresses based on yield strength and allowable stress intensity are mentioned in Table 3. 6. Results of the analysis Two load cases have been considered. First is the atmospheric pressure acting o
35、n VV/CS assembly with self-weight (no baking) and the second is the combined thermal (baking) analysis with tem- perature distribution as input body loads coupled with structural loadings. Structural results (no baking) Maximum deection (Fig. 3a) at top and bottom cryostat trian- gular
36、port 8.9 mm. Deection should be kept with in 1/2t 7 by increasing thickness of plates to prevent large deection effects. Membrane stress (Fig. 3b) for all components (over majority of cross-section area) is about 50 MPa less than 1.0SM (187 MPa) of SS 304L. Local membrane stress at geometric discont
37、inuity, thick- ness variation locations in components is 185 MPa maximum, less than 1.5SM (281 MPa) of SS 304L. Thermal results Considering temperature dependent thermal conductivity and specic heat of SS 304L, steady state is reached approximately at 11 h and 11.4 h for 250 C (Fig. 4a) and 150 C (Fig. 4b), respectively, baking scenario considering convection/conduction only (radiation effects ignored). Fig. 3. (a) Deection results of VV/CS assembly and (b) stress pattern for VV/CS assembly.
